The owners of Chile's San Esteban mining company faced questions yesterday from a government committee about safety failures which led to the accident that has trapped 33 miners underground.

Alejandro Bohn and Marcelo Kemeny have so far failed to explain why the mine was reopened after an earlier accident on 11 July, when a rock fall severed the leg of one miner, Gino Cortés.

Speaking of those presently underground, Bohn said yesterday: "The pain caused by this unwanted, unforeseen situation warrants we ask they forgive us for the anxiety they have suffered these days. It has been a terrible situation and we hope it ends very soon."

Following July's accident the San José mine was shut to take "corrective measures". On 28 July, eight days before the recent collapse, a health official, Raúl Martínez Guzmán, signed a note allowing the mine to reopen. He resigned on Monday.

Prosecutor Héctor Mella is seeking a court order to stop Bohn and Kemeny leaving Chile while he investigates. Asked whether he would bring criminal charges against the pair, Mella said: "We'll leave that until the end. At this point nothing is decided."

In the meantime the mine's workers on the surface fear they may not be paid. The owners have repeatedly said it is "difficult" to continue to pay salaries and asked for assistance, a request the government rejected. "Have the company be in debt with the state, not with the workers," pleaded Eveyln Olmos, president of the miners' union.

After delays, engineers yesterday began drilling a rescue tunnel through 700 metres of solid rock to reach the trapped miners. Their Strata 950, a giant Australian machine, is expected to advance six metres a day. Chilean president Sebastian Piñera called it Operation San Lorenzo, in honour of the patron saint of miners.

The men have moved to a drier spot 200 metres down a tunnel from their previous camp. Constant humidity has made sleeping difficult and led to severe skin infections. With signs that they are susceptible to ailments from depression to extreme weight loss, the ministry of health has established a strict daily routine.

"We provide medication; we do tests – measure their blood pressure, temperature and waistline every day," said health minister Jaime Mañalich. "We vaccinated them, and established an adequate daily supply of water and food so they can begin to recover."In what he called an end to a period of "stabilisation", Mañalich announced the priority was now to keep the men under constant medical supervision during their estimated three-month wait for rescue.

A team of Nasa scientists is on the way to Chile from the United States to help with routines to stave off medical and mental problems.

"We think some of the things we learned [in space] can be adapted," said one.